1. Field of the Invention
This application relates to integrated circuit devices more particularly to temperature compensation in integrated circuits.
2. Description of the Related Art
Clock sources typically utilize a resonator such as a crystal oscillator or surface acoustic wave (SAW) device. Clock sources such as crystal or SAW oscillators (XO/SO) and voltage controlled crystal or SAW oscillators (VCXO/VCSO) are common clock sources. Because the stability of clock signals generated by the XO/SO and VCXO/VCSO devices may be affected by variations in temperature, it is common to adjust the clock output signals provided by such devices based on temperature in order to try and obtain stable outputs over temperature.
Referring to FIG. 1, a prior art temperature compensation technique is illustrated in which a temperature sensor 101 is utilized to detect a temperature. The detected temperature is used to retrieve one or more adjustment values corresponding to the detected temperature in a look up table 103. The retrieved value(s) are processed in an algorithm block 105, e.g., to interpolate the appropriate correction value based on the detected temperature and retrieved adjustment value(s). The correction value is then converted to an analog voltage in the digital to analog converter 107. The analog voltage is then supplied to the summer 111, which also receives a normal voltage control input (not compensated for temperature) on node 112. The summing block 111 supplies the voltage controlled oscillator (VCO) 113 with a control value that is compensated for temperature. The use of the stored adjustment values, allows the device to adjust its VCO output based on temperature to ensure that frequency stability over temperature. In order to initially calibrate the device for temperature, it has been common to store the temperature compensation values in the look up table or other memory structure 103 during manufacture.
It would be desirable to provide an improved temperature compensation scheme to allow devices provide stable clock signals over temperature.